JVM oom Processing

General oom may be as follows:

1, Outofmemoryerror:java heap space;

2, Outofmemoryerror:permgen space;

3. Outofmemoryerror:unable to create new native thread

For the 1th and 2nd cases, the JVM parameters (Xms-xmx-xx:permsize-xx:maxpermsize) can be set to adjust processing.

Problem 3 occurs because we create too many threads, and the number of threads that can be created is limited, causing the exception to occur. The number of threads that can be created is calculated as follows:
Number of threads= (maxprocessmemory-jvmmemory-reservedosmemory)/(Threadstacksize)

Where: Maxprocessmemory refers to the maximum memory of a process
Jvmmemory JVM Memory
Reservedosmemory reserved Operating system memory
Size of the Threadstacksize line stacks

In the Java language, when you create a thread, the virtual opportunity creates a thread object in the JVM memory to create an operating system threads, and the system thread's memory is not jvmmemory, but the remaining memory in the system (Maxprocessmemory- Jvmmemory-reservedosmemory).
with the above example, let's illustrate the formula:
     Maxprocessmemory under 32-bit Windows is 2G
    jvmmemory   Eclipse The program memory that is started by default is 64M
    reservedosmemory  is generally around 130M
  formula is as follows: (2*1024*1024-64*1024-130*1024)/325 = 5841
  formula calculated 5841, and practice 5602 basically consistent (biased because reservedosmemory is not very accurate)

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Gee, a little bit of our common sense, well, let us verify, still use the above test program, plus the following JVM parameters, the test results are as follows:

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 a) if there is a bug in the program that causes the creation of a large number of unwanted threads or the thread is not recycled in a timely manner, the bug must be fixed and the parameter modification cannot solve the problem;
 b) If the program does require a large number of threads and the existing settings do not meet the requirements, you can increase the number of threads that can be created by modifying the maxprocessmemory,jvmmemory,threadstacksize three factors:
     maxprocessmemory using 64-bit operating systems
    JVMMemory   Reduce jvmmemory allocations
    threadstacksize  reduce the stack size of a single thread

JVM oom Processing